Manufacture of synthetic rubber



Patented May 30, 1950 2,509,664 MANUFACTURE SYNTHETIC Fred H. Amon,westonyand Fred SfThornhill,

Hyde Park, Mass, assignors to"Godfrcy L. Mass, a corporation olf Cabot,Inc, Boston li i' l ie r i sl No ljrawing. Original application February6, 1943, Serial NO 475,050. Divided all rli etion No emb 1944, T Q-. $3

This invention consists in new composition of matter, 'v iz.hydrophiliccarbon black produced by treating carbon black w'ith sodiumhypo chlorite, a product having "characteristics not found in any carbonblacks heretofore available to the industry and adapt it for use in newfields of industry. The" invention includes Within its scope certainnovel rubber and yn. thetic rubber products containing hydrophiliccarbon laclg and th'e'no'velproce's's herein dis closed forproducing thA Carbon batsman various forms heretofore known is naturally hydrophobicand organophilic, that is, it preferentially"disperses in non- P 13substan sums zenswh r s it a been impractical eigcept thegreatest'difficulty to form even tern ary"suspen"sion's of carbon blacl; 'in"aqueousfsoluti ons. this account it has provedirripracticableheretofore to disperse carbonbl ck 1n either'naturalbrsyn- "theti'crubber latex." "Previous attempts have failed due to the fact thatstandard"grades" of carbon black very completely precipitated" the latexhydrocarbon from"the""'serum.* 1

' We have discovered-thatbytreating carbon black with a wetersoiunqn 'of"s'odilim'liypoc'hlorite, or by ectin'g itto"elctrolysisin a solution ofsodi "chlojide, er'by' suspending 'the black" in a Water Soliit' ofsodium hydroxide and adding chlorine "gaslt ispos'fsible radically toalter acumen 'propertiespf carbon black so that it willrea'dilyandspontaneouslydisperse to form an excellent" st tle's'uspe sionin'waterl This new ucrnas, ag ongothers, the'valuable and unpredi ablechar teristic of entering into 2 clai s. (01. zen-41.5)

complete dispersion with water and forming therewith an ink which cannotbe washed from news print with'water alonebut can be readily andcompletely removed by a dilute calcium hypochlorite solution. When a 5%or water suspension of this new hydrophilic carbon black acetic acidand'inaking a, microscopic examination of the coagulated material.

One process for producing the novel carbon black of our inventionisagitated carbon black in a water solutionofsodium chloride and thensubject the solution to electrolysis.

During this action chlorine is'r'reely evolved and a considerableconcentration of sodium hypochlorite is built up in the solution. Uponremoving the carbon black and drying it, the resulting product is foundto have'striking water-dispersing characteristics? In"many instancesthecarbon black itself; during air "drying? takes on a re markablebluesheenb An alternative process for producing the same resultsconsists in subiecting the carbon bla'clrof commerce to'vi'gorous"OXidiZingbOnditionS: at substantially room temperaturethrOUgh "the medium "of sodium hypochlorite. One "satis factoryprocedure "consists instirring 100 grams of "carbon blackwith300=cwc. ofwater-and 300 c; cfof 10%sodiiiin hypochloritesolutionat'a temperatureof C. 'A violent exothermic re actiori' occurs. Thesludgeisthen'acidified-with hydrochloric acid, and the sodium chlorideand excess hydrochloric 'acid is washed out? The carbon black may thenbe separated from the sludge by "centrifuging; filtering-and air *dryingat a temperature of less than 1GU9C.- On the addition ofafew drops'of'ammonia this carbon black product will' at =once-enter into-completedispersion with Water forming a satisfactory ink;

Gastex carbon black, P 33 blackyand acetylene black; or finelygro'uhdcharcoal;although normally hydrophobic, cantby this treatment beconverted 'into-hydro'philic productsr *Carbon blacks of theCarbblactype, commonly used in lacquers, react instantlyandextremelyviolentlywith a solution of' sodium hypochlorite "and require asomewhatlarger'amount oithe latter'to effect a complete transformationto Water-disbersime form." 1' Dispersible carbon black produced as aboveoutlined is ofvalue as"a=reinforcin"g agent for synthetic "rubber;"andmay be incorporated with thelate'x, forexarnp'le, to such ame'xtentthat'the carbon black constitutes up' to 35%=o'fthe weight of the totalhydrocarbon content of -thelatex Without coagulatingthe'latexx Infact,,-the compound thus produced is the full equalof'any syntheticrubber compound in which 1 the same percentage 'of "carbon "black in adry statehas been in'co'rp'orateilby milling-L" It' is "noted that thedispersion of the carbon black in the'rubber latex" is not entirelycomplete"since particles are clearly visibleat a'magnification or 1300'di- 'a'meters.

The water-dispersible black used in the paste product may beprepared-from Grade" El Spheron. A" satisfactory/formula "calls for IOOgramsof this carbon black td'be treated'with 300 c. c. ofwater and 300 c.c. of 10%hypochlorit solution. This mixture forms a 'sl'ud'ge whichshould be allowed to stand for about 24 hours for complete reaction. ThepH of the sludge is 8-9. Hydrochloric acid is next added to acidify thesludge to a pH of about 2, and in the illustrative formula about 10 c.c. of concentrated hydrochloric acid is required. The treated carbonblack is then washed with about 500 c. c. of water to remove the NaClformed in the reaction, and any excess of HCl. The presence of NaCl orexcess acid interferes with the desired water-dispersing characteristicsof the product. When they are removed by washing as indicated above, thecarbon black begins to disperse in the wash water and go through thefilter. At this point, therefore, the washing should be stopped and theblack paste allowed to dry at a temperature of not over 100 C.

The finished carbon black product contains about 5% water and dryingshould be carried out at temperatures suificiently low to permitretention of substantially this amount of moisture; otherwise when theproduct is heated to complete dryness, its dispersibility is lost orsubstantially reduced. The dried carbon black product containing about5% water may then be pulverized. For redispersion of the carbon black inwater a pH of 8-9 is the optimum condition for a material prepared asdescribed in the above example. However, by the use of finer particlesize blacks, such as Carbolac, or by the use of larger quantities ofNaOCl to obtain more thorough oxidation, or both, blacks can be preparedwhich disperse spontaneously to form stable suspensions in a pH range offrom 3.0 to 9.0. The desired pH may be readily obtained by adding asmall amount of ammonia to the water. On adding the dry carbon blackproduct to water, an excellent dispersion is at once obtained withoutstirring or grinding.

In making the paste product of our invention 30% to 60% of our novelhydrophilic carbon black in water gives a stiff paste which closelyresembles in appearance and properties the special graphite pasteheretofore available only at greatly increased cost.

In producing the hydrophilic carbon black of our invention very littleif any change can be detected in the surface area of the finishedproduct as compared to that of the starting carbon black. This is anunexpected characteristic since carbon black oxidized by gaseoustreatment exhibits a striking increase in surface area.

The hydrophilic carbon black of our invention is of great importancewhen used as an ingredient for synthetic rubber; first, because it canbe compounded with the various synthetic rubber latices and reinforcesthe resulting compound, and, second, because it impart a, very desirablesoftness and tack to the rubber-like copolymer of butadiene and styreneknown as Buna S and other synthetic compounds. Buna S is otherwisedeficient in tack.

Hydrophilic carbon black prepared as above explained may be added to thelatex of Buna S or other synthetic rubbers in amounts giving, forexample, 10 to 35% carbon black loading of the resulting rubber compounddepending on the characteristics of the compound desired. Thehydrophilic carbon black, when mixed with the latex by stirring, readilyforms a satisfactory dispersion throughout the latex and the mixturethus formed may be then processed by the conventional steps usuallypractised in the manufacture of synthetic rubbers.

The necessity of adding organic wetting agents 4 to the latex, whichwould otherwise be required, is obviated by employing hydrophilic carbonblack in the manner above outlined, and appreciable saving in the costof manufacture is made for this reason.

Sodium hypochlorite, NaOCl, used in carrying out the process of ourinvention, may readily be prepared by saturating a solution of NaOl-Iwith C12, 1. 8.,

Sodium hypochlorite has been specifically mentioned in the foregoingdescription but potassium hypochlorite or other hypochlorites of thesodium or alkali earth groups may be employed as equivalents or partialequivalents with appropriate modification of the illustrative process.The essential reaction of the process is oxidation of the carbon blackin the presence of moisture. One of the most economical ways of bringingthis about is merely to bubble chlorine gas through an alkaline solutionhaving carbon black present therein and so create a hypochlorite in thepresence of the wetted carbon black to be treated.

The present application is a division of our prior application Ser. No.475,050, filed February 6, 1943, now Patent No. 2,439,442 dated April13, 1948.

Having thus disclosed our invention and described two related processesof producing the novel product thereof, we claim as new and desire tosecure by Letters Patent:

1. In the compounding of rubber, the steps of adding a 5-10% watersuspension of carbon black, which is hydrophilic and has been renderedhydrophilic by being reacted with sodium hypochlorite, to the latex ofthe rubber being compounded, thereby producing a stable dispersionwithout coagulation which is substantially free from dispersing agent,and then precipitating the rubher and carbon black content by acidifyingthe mixture.

2. In the compounding of rubber-like copolymers of butadiene andstyrene, the steps of adding a 5-10 water suspension of carbon black,which is hydrophilic and has been rendered hydrophilic by being reactedwith sodium hypochlorite, to the latex of the said rubber-likecopolymer, thereby producing a stable dispersion without coagulationwhich is substantially free from dispersing agent, and thenprecipitating the rubber-like copolymer with the carbon black dispersedtherein by acidifying the mixture.

FRED H. AMON. FRED S. THORNHILL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS- Number Name Date 1,818,770 Tuley Aug. 11, 19312,178,382 Wiegand Oct. 31, 1939 FOREIGN PATENTS Number Country Date523,149 Great Britain July 8, 1940 OTHER REFERENCES Pages 423 to 427,The Rubber Age, Feb. 1944. Pages 577 to 582, The Rubber Age, Sept. 1944.

2. IN THE COMPOUNDING OF RUBBER-LIKE COPOLYMERS OF BUTADIENE ANDSTYRENE, THE STEPS OF ADDING A 5-10% WATER SUSPENSION OF CABRON BLACK,WHICH IS HYDROPHILIC AND HAS BEEN RENDERED HYDROPHILIC BY BEING REACTEDWITH SODIUM HYPOCHLORITE, TO THE LATEX OF THE SAID RUBBER-LIKECOPOLYMER, THREBY PRODUCING A STABLE DISPERSION WITHOUT COAGULATIONWHICH IS SUBSTANTIALLY FREE FROM DISPERSING AGENT, AND THENPRECIPITATING THE RUBBER-LIKE COPOLYMER WITH THE CARBON BLACK DISPERSEDTHEREIN BY ACIDIFYING THE MIXTURE.